The invention relates to improvements in machines for kneading, stirring and/or otherwise mixing and agitating liquid, flowable solid and/or viscous materials. More particularly, the invention relates to improvements in upright mixing machines of the type wherein one or more vertical or substantially vertical mixing tools extend downwardly beyond a housing and into a vessel which contains a batch of miscible material or materials.
It is already known to provide an upright mixing machine with a gear case which is rotatably mounted in the housing at a level above the vessel and supports one or more tools (e.g., one or more tools which have mixing elements in the form of blades) in addition to containing bearings, gears, seals and other parts which are used to rotate the tool or tools, to properly mount the tool or tools in the gear case, as well as to prevent penetration of mixcible material or materials from the vessel into the gear case and/or into the housing. It is also known to install the gear case in such a way that it can be removed from the housing of the upright mixing machine. If the gear case supports two or more tools, the tools normally include a centrally located tool which can be rotated about its own axis and one or more lateral or outer tools which are rotatable about their own axes and can also orbit about the centrally located tool. The gear case then constitutes the carrier of a planetary transmission which is installed in the housing to rotate the tools about their own axes as well as to orbit the outer tool or tools about the centrally located tool. The sun wheel or wheels and the planet wheel or wheels of the transmission are or can be mounted in the interior of the hollow gear case. The means for rotating the gear case (planet carrier) about its own axis (which normally coincides with the axis of the centrally located mixing tool) includes a motor and a gear train between the output element of the motor and the gear case. Rotation of the gear case entails rotation of each mixing tool about its own axis and orbital movement of the outer tool or tools (if any) about the centrally located tool. The planetary transmission can include two units one of which serves to orbit the outer tool or tools about the centrally located tool and the other of which serves to rotate the centrally located tool in response to composite orbital and rotary movement of the outer tool or tools. The arrangement is such that, if the lower end portions of the mixing tools carry blades or analogous mixing elements, the paths of circular movement of radially outermost portions of the blades cross each other when the centrally located tool rotates about its own axis while the outer tool or tools rotate about their respective axes and simultaneously orbit about the centrally located tool, but such movements of the tools do not entail any clashing of the blades.
As a rule, the housing and the vessel of a standard upright mixing machine of the above outlined character are installed at a level well above the floor level or above the level of the base of the machine frame. This renders it possible to raise a vessel, which contains a fresh batch of material to be mixed, toward the underside of the housing so that the mixing element or elements of the mixing tool or tools enter the vessel from above as the vessel is caused to move upwardly. When the mixing of a batch is completed, the vessel is lowered and is ready to be relieved of its contents or to be replaced with a vessel containing a fresh batch. Such mixing machines are used extensively for the making of tough plastic masses of doughy consistency from liquid, flowable solid and/or viscous materials. For example, the ultimate product can constitute a propellant or an explosive.
A drawback of presently known upright mixing machines which are used for the making of explosives, propellants and/or other dangerous or potentially dangerous products is that cleaning, inspection, maintenance and/or replacement of tools and/or other parts takes up inordinately long periods of time. On the other hand, such work must be performed at frequent intervals because penetration of a propellant or explosive into and accidental combustion in the gear case and/or housing can result in extensive damage to or in total destruction of the machine or of a portion of or the entire plant, and in injuries to attendants or fatal accidents. As a rule, a mixing machine which is used for the making of explosives or propellants must be inspected and thoroughly cleaned at regular intervals. For example, the persons in charge must ensure that no explosive has penetrated between the teeth of mating gears, into the bearings for the mixing tool or tools, or between other parts (such as the gear case and the housing) which move or are likely to move relative to each other when the machine is in use. Such mixing machines normally comprise various static and dynamic seals which must be inspected at frequent intervals in order to ensure timely detection of leakages. The same applies for the backlash or flank clearance between the teeth of mating spur gears, bevel gears, worms and worm wheels and other torque transmitting components. The absence of excessive flank clearance is particularly important when the mixing machine comprises several mixing tools and the blades or otherwise configurated mixing elements of the tools must rotate and/or orbit without clashing and without coming in contact with the vessel.
The reason that the inspection of a conventional mixing machine is a time-consuming operation, which necessitates long periods of idleness of the machine, is that the gear case and the parts which are carried by the gear case must be lifted above the housing in order to afford access to those parts which must be cleaned, inspected, serviced and/or replaced. Moreover, the inspection can be carried out only if there is ample space above the housing of the mixing machine, not only for the lifted gear case but particularly for the lifting equipment (e.g., a crane) which is used to raise the gear case above and out of its housing. While the mounting of the gear case from above, or the removal of gear case from the housing by moving the gear case upwardly, does not necessarily create problems in the plant in which the mixing machine is assembled, a plant in which the mixing machine is put to use is much less likely to provide adequate space at a level above the housing and/or to have adequate equipment which can be used to carry out such operation. The situation is aggravated due to the fact that the height of an assembled upright mixing machine is considerable because, and as mentioned above, the machine must be designed to provide room for moving the vessel up and down in the space beneath the housing for the gear case. As a rule, the gear case can be lifted above and out of the housing only if the available space above the housing is several meters high. This provides room for an overhead crane or another suitable lifting machine and for the gear case and the mixing tool or tools in raised position of the gear case. Such substantial amount of space above the mixing machine is not always available (in fact, it is hardly ever available) in a plant wherein the machine is or is to be put to use.
Another drawback of presently known upright mixing machines is that the gear case and its tool or tools can be withdrawn from and reinserted into the housing only by highly skilled operators. One of the main reasons that highly skilled operators must be called to perform such work is that an unskilled person, or a person not fully familiar with the mixing machine, is likely to damage delicate seals which are interposed between the working chamber (for the rotary and other parts of the means for rotating, orbiting and journalling the mixing tool or tools) and the (mixing) station for the exposed part or parts of the mixing tool or tools and for the vessel which contains the batch of material or materials to be mixed.
Applicant is aware of disclosures in German Pat. No. 918,925 and U.S. Pat. No. 3,151,847 which disclose mixing machines with rotary gear cases. The gear cases of the patented mixing machines do not permit convenient observation of the parts in the gear case.